• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.6
• /
• pp.767-776
• /
• 1985

Unsteady thermally stratified flow caused by two-dimensional surface discharge of warm water into a oblong channel was investigated. Experimental study was focused on the rapidly developing thermal diffusion at small Richardson number. The basic objective were to study the interfacial mixing between a flowing layer of warm water and an underlying body of cold water and to accumulate experimental data to test computational turbulence models. Mean velocity field measurements were carried out by using NMR-CT (Nuclear Magnetic Resonance-Computerized Tomography). It detects quantitative flow image of any desired section in any direction of flow in short time. Results show that at small Richardson number warm layer rapidly penetrates into the cold layer because of strong turbulent mixing and instability between the two layers. It is found that the transfer ofheat across the interface is more vigorous than that of momentum. It is also proved that the NMR-CT technique is a very valuable tool to measure unsteady three dimensional flow field.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.4
• /
• pp.111-117
• /
• 2004

An analytical study was carried out to evaluate the regenerative cooling characteristics in the liquid rocket engine of a 10tf-thrust level using kerosene as a fuel. As a supplementary cooling method, a radiative cooling was applied to the nozzle extension. It was found out from this work that the cooling system with the regenerative and radiation cooling only is not adaptable for the liquid rocket engine of a 10tf-thrust level using kerosene as a fuel for the $2^{nd}$ stage of the space launch vehicle, with the viewpoint of the thermal and thermo-structural instability and the excessive pressure drop in the cooling channel.

• Journal of the Society of Disaster Information
• /
• v.11 no.4
• /
• pp.581-588
• /
• 2015

This study was conducted by utilizing simulation (FDS6) the fire characteristics of the flammable substances such as cable compartment of a small space in the EPS room type. In the partitioned space of a room EPS supply of oxygen does not facilitate the combustion of the upward-sloping curve, as in a standard fire curve is not observed. Simulation results in a situation where ventilation is limited to the heat release rate and smoke emission characteristics of the fire showed a complex and unstable form a repeating rise and fall. Fire time was longer than the fire load. Change in the smoke emission than the heat release rate is slow, but changes of the overall surface was found to exhibit affinity.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.21 no.6
• /
• pp.49-56
• /
• 2017

The current study has developed an in-house 3D FEM code in order to model thermoacoustic problems in an annular system and compared the acoustic field calculation results with measured ones from a benchmark combustor. From the comparison of calculation results with the measured data, the current acoustic code could successfully capture the various acoustic mode found in the annular system. In addition, it was found that the transverse waves in the combustor were strongly affected by the nozzle acoustic impedances, as well, the pressure distributions were closely related with the combustor acoustic pressure field.

• Journal of the Korean Chemical Society
• /
• v.24 no.6
• /
• pp.457-462
• /
• 1980

Phosphates and phosphoric amides were synthesized by the reaction of phosphoryl chloride with allyl alcohol, 2,3-dibromopropanol, 2-pyrrolidone and ethylenimine. All of these compounds were thermally very unstable. Allyl phosphorodichoridate and diallyl phosphorochloridate gave significant amount of polymeric products when they were distilled. IR spectra showed characteristic P=O stretching bands between 1300 and $1200 cm^{-1}$ and NMR spectra were very complicated due to the long range coupling effect of phosphorus atom. And mass spectrum of 2,3-dibromopropyl phosphorodichloridate gave no indication of molecular ion peak.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1993.04a
• /
• pp.80-84
• /
• 1993

공기베어링은 기체으 압축성에 의한 평균화 효과로 운전정밀도가 우수하고 기체의 낮은 점도에 의한 효과로 마찰력과 열발생량이 매우 적으며, 사용가능 온도구간이 저온에서 고온까지 넓고 프로세스 계통내의 기체를 윤활제로 사용할 수 있기 때문에 그 경우 불순물에 의한 오염이 문제되지 않는 장점등이 있다. 이와 같은 특성과 더불어 공기베어링은 지지 물체를 완전히 부상시켜 운전하므로써 마찰$\cdot$마모와 온도변화에 다른 열변형이 문제되지 않는다. 이러한 장점으로 인해서 공기베어링은 현재 정밀기기의 미끄럼면, 각종 측정장치의 테이블지지 기구로 많이 사용되고 있다. 반면 공기베어링의 단점으로는 기체의 낮은 점성계수로 인해서 부하능력이 적고 강성, 감쇄계수 또한 적다. 그리고 기체의 압축성으로 인해 뉴메틱 헤머라는 불안정 현상이 생기기도 한다. 본 연구에서는 스퀴즈 효과를 이용한 능동 공기베어링을 설계, 제작하여 실험하였다. 본 연구의 목적은 강성과 감쇄 계수가 작은 공기 베어링의 단점을 보완하기 위해 드러스트베어링을 대상으로 능동베어링을 설계, 제작하여 그 특성을 연구하고 기초 설계자료를 축적하는데 있다.

• Applied Biological Chemistry
• /
• v.29 no.2
• /
• pp.207-211
• /
• 1986

Lactic acid bacteria isolated from Kimchi were tested for inhibitory activity against E. coli, Streptococcus faecalis and Lactobacillus bulgaricus. The inhibitory strains appeared most frequently around the middle stage of fermentation during two weeks of observation, and the majority of them were identified as Pediococcus cerevisiae. The agent(s) responsible for the inhibitory activity of P. cerevisiae was inactivated by heat treatment at moderate temperature, but resistant to proteolytic enzymes. The production of the inhibitory compound(s) decreased when the pH of the medium was maintained at about 7 with phosphate buffer.

• Journal of Welding and Joining
• /
• v.9 no.3
• /
• pp.10-17
• /
• 1991

용접구조물에서 용접이음부가 차지하는 비율은 매우 작은 경우가 많지만 용접이음부에는 각종 초기결함(이들 결함으로부터 진전하는 피로 균열, 환경에 의한 균열등을 포함) 및 용접 초기의 부정형을 비롯해서 형상적 불연속 등에서 유기되는 국부적인 응력, 변형률의 집중, 잔류응력, 구속응력, 용접금속이 갖는 숙명적인 야금적 특성의 불균일, bond부 및 HAZ부에서의 용접열 싸이클에 의한 재질의 국부적 강도저하등 용접부의 강도를 저하시키는 인자들이 복합되기 쉽고, 용접구조물 전체의 내파괴 건전성평가에서 용접부가 파괴 강도는 매우 중요하다. 용접구조물의 설계, 시공의 목적은 소요성능의 확보에 있고 구조물이 사용중에 성능손실이나 불안정 파괴가 발생하지 않도록 하는 것이 주요요건이 될 것이다. 현재의 제강기술수준에서 볼 때 모재의 강 도보다 오히려 용접부의 강도 특히 피로강도 및 파괴 인성을 적절하고 합리적으로 평가하는 것이 매우 중요하다고 해도 과언이 아닐 것이다. 용접부의 강도를 평가하는데 있어서 용접부에 발 생하는 용접결함에 대한 평가는 매우 중요하며 이들 결함에 대한 허용결함한계를 평가하여 보수 여부 및 용접구조물의 신뢰성을 평가 할 필요가 있다.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.13 no.6
• /
• pp.284-289
• /
• 2003

The electric furnace, inside which the desired temperature is kept by the generated heat, is known to be a difficult system to control and model exactly because system parameters and response delayed time are varied as the temperature and positions are changed. In this study, the GPCEW (generalized predictive control with exponential weight), which always guarantees the stability of the closed loop system and can be effectively applied to the internally unstable system, was introduced to the ceramic drying electric furnace and was verified by showing its temperature tracking performance experimentally.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.07b
• /
• pp.790-793
• /
• 2004

이중의 망간 perovskite 블록을 가진 Ruddlesden-Popper 상(R-P phase) $Sr_3Mn_2O_7$ 은 공기중에서 불안정하다. 본 연구에서는 망간 이온 자리에 철 이온을 소량 치환 함으로써 R-P 상을 안정화 시켰으며 이들의 결정구조는 X-선회절 데이터를 이용하여 Rietveld 법으로 정밀화하였다. 안정화에 필요한 Fe 이온의 양은 약 x=0.15로 나타났으며 Fe이온의 양이 증가함에 따라 쉽게 안정화 되었다. 자화율 측정결과 x=0.20 시료는 120K에서 paramgnetic-antiferromagnetic 전이를 나타내었고 이 전이 온도는 치환되는 Fe이온의 양이 증가함에 따라 감소하는 경향을 나타내었다.